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Category: raspberry-pi

Here’s the Raspberry Pi temperature code

Posted on April 25, 2020April 27, 2020 by David

To add temperature to the frame caption, I first do a check to see that it is running on a Raspberry Pi. This function does that.

void SetPiFlag() {
	struct utsname buffer;
	tempFlag = 0;
    if (uname(&buffer) != 0) return;
    if (strcmp(buffer.nodename,"raspberrypi") !=0) return;
	if (strcmp(buffer.machine,"armv7l") != 0) return;
	piFlag=1;
}

Note you have to add this include

#include <sys/utsname.h>

Now you need to call this function to return the temperature as a float.

float ReadPiTemperature() {
    char buffer[10]; 
	char * end; 
	if (!piFlag) return 0.0f;
	if (SDL_GetTicks() - tempCount < 1000) {	
		return lastTemp;
	}
	tempCount = SDL_GetTicks() ;
	FILE * temp = fopen("/sys/class/thermal/thermal_zone0/temp","rt"); 
	int numread = fread(buffer,10,1,temp); 
	fclose(temp); 
	lastTemp = strtol(buffer,&end,10)/1000.0f;
	return lastTemp;
}

Things to notice.

If it’s not running on a Pi it always returns 0.0C.
No matter how often it’s called, it only reads the temperature once a second.
In between reads it caches the temperature in a variable lastTemp

When I first wrote this, it was reading the temperature on every frame. It actually changes that quickly but that made it hard to read. So once a second is fine.

Asteroids now runs on a Pi 4

Posted on April 24, 2020April 24, 2020 by David

I was interested in seeing what frame rate I got out of it and how much it warmed the PI.

The change to get the texture loaded was to split the five image files (four x asteroid + player ship) into two rows each.

I added this code into the DrawPlayerShip function.

    if (Player.dir >= 12) {
	  	spriterect.y = SHIPHEIGHT;
		spriterect.x -= SHIPWIDTH*12;
	}

So for directions 0-11, it uses the top row and 12-23 the 2nd row. There’s similar code in the DrawAsteroids function.

I’m getting about 55 fps, twice the frame rate of the 3B+. Sustained play over five minutes got the temperature up to 51C, but if I start the game and let asteroids drift about for a while it settles somewhere around 48-50C.

I have a fan fitted plugged into the 3.3V that runs all the time but is almost inaudible. There’s also a 5V setting that can be used for extra cooling but you only need that when temperatures get up to the 80C mark. There’s also 3 copper heat sinks stuck on three chips on the motherboard.

It’s very playable at 55 fps. This isn’t full screen BTW but on a 1024 x 768 playing area. There’s just one last change I’ve added. I combined the uname code to detect if it is running on a Pi and in that case display the temperature on the Window caption. If you look closely at the image above you’ll see it says 43.82 C. I use a counter and check against so it only reads the temperature once a second and caches the result.

Two bugs on Raspi – one fixed

Posted on April 23, 2020April 16, 2020 by David

As always bugs are the fault of the creator and mea culpa (my bad!). I can trace this back to my conversion from the Windows source to the Ubuntu version. This line in LoadMask

int numread = fread_s(mask, sizeofmask, sizeofmask, 1, fmask);

Became this line in the Ubuntu version.

int numread = fread(mask, sizeofmask, sizeofmask, fmask);

But should have been this instead.

int numread = fread(mask, sizeofmask, 1, fmask);

It affected numread and failed just on the masks/am2.msk load.
The other bug only applies on Raspberry Pi 4 and is a limitation of the implementation of SDL2 texture size.
One of the asteroids graphics is 6720 x 280 and the error it returns is Textures can’t be bigger than 4096×4096.

What is odd that it works on a Raspberry Pi 3B+ but not on the 4 which has 4 GB of RAM. Anyway I’m writing a program to transform the graphics from 24 x 1 shapes to 12 x 2. So the 280 x 280 shape file will be 3360 x 560. This will affect the player ship and all asteroids and need a slight change to the DrawPlayerShip() and DrawAsteroids() functions.

Fun with Raspberry Pi 4

Posted on April 21, 2020April 12, 2020 by David

Bugs! — Image by Ron van den Berg from Pixabay

So it turned up and I setup things up similar to the 3B+. My interest was in seeing what frame rate it can manage compared to the 27 FPS that the 3B+ managed.

When I eventually got Clang, VS Code etc. installed and setup, compiled etc. it crashed just like it did on the 3B+ when first run. And again it failed to load the am2.msk file; I will really have to figure out what’s going on there. But also it would now not load the a1.png image. This is the one with the 24 x 280 x 280 asteroid images.

SDL provides a function SDL_GetError so I added that to the output when an image file fails to load. The error message that came back was Texture dimensions are limited to 4096×4096. Now this is weird for this Pi has 4 GB of RAM (the 3B+ has 1GB) and is outputting on the same 24″ monitor that the 3B+ used as well. Now it’s true that the a1.png file has dimensions of 6,720 x 64, so I can understand why that would cause grief but not why it worked on the 3B+. I suspect it has to do with RAM being allocated between the GPU and CPU so I’ll check that out.

I also installed Clang-6.0 to try that. On the Pi, installing clang defaults to Clang-7 (they changed the name so it no longer has a .0 on the end!). The release notes for Clang-7 suggested a possibility to do with abi incompatibility between Clang-7 and earlier versions. Bit of a longshot but I thought, that might explain the fail to load am2.msk file but no joy.

Well there’s nothing like juicy tender bugs to get my teeth into… the battle is on.

How to read a Raspberry PI temperature in C code

Posted on April 20, 2020April 12, 2020 by David

Reading the temperature of a Raspberry PI can be done in a couple of ways. This command:

vcgencmd measure_temp

Outputs something like temp=32.7’C. My 3B+ PI has heatsinks and a cooling fan so runs cool. Even with asteroids it only peaked at 50.5C. Well below the throtle back temperature of 85C.

Another way (I suspect they are the same) is to do

cat /sys/class/thermal/thermal_zone0/temp

Which outputs values like 32705. Just divide by 1000 to get the temperature in Celsius.

But how do we do it in code? Well I’ve tested this code below and it seems to work.

#include <stdio.h>
#include <stdlib.h>
#include <strings.h>

int main(void) {
  char buffer[10];
  char * end;
  FILE * temp = fopen("/sys/class/thermal/thermal_zone0/temp","rt");
  int numread = fread(buffer,10,1,temp);
  fclose(temp);
  printf("Temp = %5.2fC\n",strtol(buffer,&end,10)/1000.0);
}

It reads the device as a string then converts to a long using strtol and divides that by 1000 then prints it. Output is something like:

Temp (C) = 34.88C

Now it just needs combined with the code to detect that it’s running on a Pi and you’re good.

Identifying a Linux system in code

Posted on April 19, 2020April 12, 2020 by David

Since I got asteroids running on a Raspberry Pi, I have decided I want to incorporate the temperature in the window caption when you switch it to debug mod by pressing Tab. Currently all that does is display position info on moving objects and bounding boxes.

But if I include that code in, I want to be sure that it only works when running on a Raspberry Pi. So I need some code to identify the system. A bit of digging and I discovered the Linux uname command. That link goes to an online man page for uname.

If I run uname -a on my Ubuntu 18.04LTS I get this.

Linux david-Virtual-Machine 4.15.0-96-generic #97-Ubuntu SMP Wed Apr 1 03:25:46 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

And on my PI.

Linux raspberrypi 4.19.97-v7+ #1294 SMP Thu Jan 30 13:15:58 GMT 2020 armv7l GNU/Linux

In fact the uname -n command gives david-Virtual-Machine on Ubuntu and raspberrypi on the PI. These are the names though names are often changeable and what if someone is running ubuntu on a PI? Yes it is a thing. But the uname -m identifies the CPU. x86-64 on my Ubuntu and armv71 on the pi.

I did a bit of digging and found a C program on stackoverflow that will do the same as uname.

#include 
#include 
#include 
#include <sys/utsname.h>

int main(void) {

   struct utsname buffer;

   errno = 0;
   if (uname(&buffer) != 0) {
      perror("uname");
      exit(EXIT_FAILURE);
   }

   printf("system name = %s\n", buffer.sysname);
   printf("node name   = %s\n", buffer.nodename);
   printf("release     = %s\n", buffer.release);
   printf("version     = %s\n", buffer.version);
   printf("machine     = %s\n", buffer.machine);

   #ifdef _GNU_SOURCE
      printf("domain name = %s\n", buffer.domainname);
   #endif

   return EXIT_SUCCESS;
}

And this is what it outputs on a PI.


system name = Linux
node name   = raspberrypi
release     = 4.19.97-v7+
version     = #1294 SMP Thu Jan 30 13:15:58 GMT 2020
machine     = armv7l

So that bit is easy to do. Next is getting the temperature, but that’s for another blog entry…

Building Asteroids on a Raspberry-Pi

Posted on April 17, 2020April 10, 2020 by David

Silly me completely forgot that Raspberry Pis have a different CPU architecture compared to my PC. You just get used to something working on Linux and it was only after copying and it didn’t run that I realised my mistake. So I now have to recompile Asteroids (from Chapter-48.zip).

I’ve had a Raspberry-Pi 3 B+ for a year and wanted to run the Linux asteroids on it, now that I have it working on Ubuntu.

To do that I had to setup Pi, running Raspbian downloaded from the Raspberry Pi website onto my Windows PC and then I used Win32 DiskImager (free Windows software) to burn the Raspbian OS onto a SD Card. Raspberry-Pis boot from SD Cards and the better and faster the SD card, the quicker the OS runs. Get a class 10 with A1 SD Card if you can.

After the Pi booted and Raspbian was installed and configured I had to enable SSH on the Pi; it’s disabled by default.

So now my PC was talking to the Pi using the excellent free WinSCP. I copied all the files over, including the masks, sounds and images folders and all the source code and my exe built on Ubuntu which was the wrong file type. (Trying to run Intel code on an ARM- good luck with that!)

Now it turns out that the Raspbian version I installed (I’d gone for the Raspbian Buster with desktop and recommended software-2.5 GB download) included the non-dev version of SDL2. But as I needed to recompile the whole program, I had to install Visual Studio Code, Clang and the dev versions of SDL2, image and mixer.

Visual Studio Code on Arm?

Microsoft don’t do an official version for Raspberry-Pi or other ARM boards. However I discovered that a developer called Jay Rodgers has taken their source code (VS Code is open source) and you can get a version from his site. It’s very usable on the Pi. Almost but not quite identical.

After installing the dev versions of libsdl2, image and mixer, I was almost able to compile it. I’d installed Clang but unlike the version on Ubuntu which was Clang-6, the version on Raspbian (based on Debian Buster) is Clang-7.

This means you have to edit the tasks.json file in the hidden .vscode folder. On line 25 where it says “command”: change the path to “/usr/bin/clang-7”.

That built ok, but when I ran it, it stopped with an error in the errorlog.txt file. For some reason, it failed loading the file “masks/am2.msk”. Now I’d had no errors copying files from Windows to the Pi. This had been a very intermittent problem when copying several files in one go from Windows 10 to Ubuntu running under Hyper-V. Occasionally it would come up with some weird error but usually copied OK on the second go.

Despite several attempts, I could not get it to load that mask so as a temp fix I commented the line out. This means that one of the four asteroids sizes can never collide with anything. But it now ran.

However, I’m only getting about 25-27 fps with it in the early levels, not the 60 fps that I get on Ubuntu on other hardware. Given that the bulk of the work is blitting graphics, I suspect the GPU is just a bit under powered. Apparently on the Raspberry Pi 4, the GPU is newer and twice as fast as on the 3B+ so I’ll have to try it on a 4 when I get one. But the game works and is just about playable.

Now I’ll have to try and figure out why it won’t load that one mask. This has the makings of an interesting bug…

Learn C Games

Posted on February 29, 2020May 23, 2025 by David

This blog is about C and Games programming (in C mainly). There are now two ebooks written by David Bolton, author of the Learn C Games Programming for beginners EBook. This is the Windows version, with a Raspberry Pi/Linux one now out.

The first 20 chapters introduce and teach C programming with many examples. This link is to an .mp4 of the asteroids game from the book. It’s about 90 seconds long and demonstrates all of the features of the game. High score table, rotating asteroids (four sizes), sound, explosions, ship hyper-jump and shields.

The remaining 30 chapters (20 in the Linux/Raspberry PI) builds up to full source code, about 2,000 lines, in 13 stages and I explain how each feature works and is implemented. All of the book’s source code is on Github. (Windows) or (Linux). More about me. Buy the Windows one on Amazon(UK), Amazon(US) or the Linux/Raspberry PI. (UK). You can buy the book in other regions by changing the region in Amazon to your local one.